Standardization of water consumption for extinguishing fires in high-rise warehouses.

Standardization of water consumption for extinguishing fires in high-rise rack warehouses.

Standardization of water consumption for extinguishing fires in high-rise rack warehouses

Currently, the main initial characteristics used to calculate water consumption for automatic fire extinguishing systems (AFES) are the standard values ​​of irrigation intensity or pressure at the dictating sprinkler. Irrigation intensity is used in regulatory documents regardless of the sprinkler design, and pressure is used only for a specific sprinkler type.

The values ​​of irrigation intensity are given in SP 5.13130 ​​[1] for all groups of premises, including warehouse buildings. This implies the use of a sprinkler AUP under the building roof. However, the adopted values ​​of irrigation intensity depending on the group of premises, storage height and type of fire extinguishing agent, given in Table 5.2 of SP 5.13130 ​​[1], do not lend themselves to logic. For example, for group of premises 5, with an increase in the storage height from 1 to 4 m (for each meter of height) and from 4 to 5.5 m, the intensity of irrigation with water also increases proportionally by 0.08 l/(s m2).

It would seem that a similar approach to standardizing the supply of fire extinguishing agent for extinguishing a fire should also be extended to other groups of premises and to extinguishing a fire with a foaming agent solution, but this is not observed. For example, for group of premises 5, when using a foaming agent solution at a storage height of up to 4 m, the irrigation intensity increases by 0.04 l/(s m2) for each 1 m of rack storage height, and at a storage height from 4 to 5.5 m, the irrigation intensity increases 4 times, i.e. by 0.16 l/(s m2), and is 0.32 l/(s m2). For group 6 of premises, the increase in the intensity of water irrigation is 0.16 l/(s m2) up to 2 m, from 2 to 3 m – only 0.08 l/(s m2), over 2 to 4 m – the intensity does not change, and at a storage height of over 45.5 m, the intensity of irrigation changes by 0.1 l/(s m2) and is 0.50 l/(s m2). At the same time, when using a foaming agent solution, the irrigation intensity is up to 1 m — 0.08 l/(s m2), over 12 m it changes to 0.12 l/(s m2), over 23 m — by 0.04 l/(s m2), and then over 3 to 4 m and from over 4 to 5.5 m — by 0.08 l/(s m2) and is 0.40 l/(s m2).

In rack warehouses, goods are most often stored in boxes. In this case, when extinguishing a fire, the jets of fire extinguishing agent do not, as a rule, directly affect the combustion zone (an exception is a fire on the very top tier). Part of the water dispersed from the sprinkler spreads over the horizontal surface of the boxes and flows down, the rest, not falling on the boxes, forms a vertical protective curtain. Partially, oblique jets fall into the free space inside the rack and wet goods not packed in boxes, or the side surface of the boxes. Therefore, if for open surfaces the dependence of the irrigation intensity on the type of fire load and its specific load is not in doubt, then when extinguishing rack warehouses this dependence does not manifest itself so noticeably.

Nevertheless, if we allow some proportionality in the increase in the irrigation intensity depending on the storage height and the height of the room, then the irrigation intensity can be determined not through discrete values ​​of the storage height and the height of the room, as presented in SP 5.13130 ​​[1], but through a continuous function expressed by the equation

where

• idict – irrigation intensity by the dictating sprinkler depending on the stacking height and the room height, l/(s m2);
• i5.5 – irrigation intensity by the dictating sprinkler at a stacking height of 5.5 m and a room height of no more than 10 m (according to SP 5.13130 ​​[1]), l/(s m2);
• w – coefficient of variation of the stacking height, l/(s m3);
• h– height of fire load storage, m;
• l – room height variation coefficient.

For room groups 5, the irrigation intensity i5.5 is 0.4 l/(s m2), and for room groups 6 – 0.5 l/(s m2). The storage height variation coefficient w for room groups 5 is taken to be 20% less than for room groups 6 (similar to SP 5.13130). The value of the room height variation coefficient l is given in Table 2.

When performing hydraulic calculations of the AUP distribution network, it is necessary to determine the pressure at the dictating sprinkler based on the estimated or standard irrigation intensity (according to SP 5.13130). The pressure at the sprinkler corresponding to the required irrigation intensity can only be determined based on the family of irrigation diagrams. But sprinkler manufacturers, as a rule, do not provide irrigation diagrams. Therefore, designers experience inconvenience when deciding on the design value of the pressure at the dictating sprinkler. In addition, it is unclear which height to take as the estimated one for determining the irrigation intensity: the distance between the sprinkler and the floor or between the sprinkler and the upper level of the fire load. It is also unclear how to determine the irrigation intensity: on the area of ​​a circle with a diameter equal to the distance between the sprinklers, or on the entire area irrigated by the sprinkler, or taking into account mutual irrigation by adjacent sprinklers.

For fire protection of high-rise rack warehouses, sprinkler AUPs are now widely used, the sprinklers of which are placed under the warehouse roof. Such a technical solution requires a large flow rate of water. For these purposes, special sprinklers are used, both domestically produced, for example, -17, -25, and foreign, for example, ESFR-17, ESFR-25, VK503, VK510 with an outlet diameter of 17 or 25 mm. In the STO [2] for sprinklers, in the brochures for ESFR sprinklers from Tyco [3] and Viking [4], the main parameter is the pressure at the sprinkler depending on its type (-17, -25, ESFR-17, ESFR-25, VK503, VK510, etc.), on the type of stored goods, the height of storage and the height of the room. Such an approach is convenient for designers, because eliminates the need to search for information on irrigation intensity.

At the same time, is it possible to use some generalized parameter to assess the possibility of using any sprinkler designs developed in the future, regardless of the specific sprinkler design? It turns out that it is possible, if we use the pressure or flow rate of the dictating sprinkler as the key parameter, and the irrigation intensity over a given area at a standard sprinkler installation height and standard pressure (according to GOST R 51043 [5]) as an additional parameter. For example, we can use the irrigation intensity value obtained without fail during certification tests of special-purpose sprinklers: the area over which the irrigation intensity is determined is 12 m2 for general-purpose sprinklers (diameter ~ 4 m), for special sprinklers — 9.6 m2 (diameter ~ 3.5 m), sprinkler installation height is 2.5 m, pressure is 0.1 and 0.3 MPa. Moreover, information on the irrigation intensity of each type of sprinklers obtained during certification tests must be indicated in the passport for each type of sprinkler. With the specified initial parameters for high-rack warehouses, the irrigation intensity must be no less than that given in Table 3.

The true irrigation intensity of the AUP during the interaction of adjacent sprinklers, depending on their type and the distance between them, can exceed the irrigation intensity of the dictating sprinkler by 1.5-2.0 times. With regard to high-rack warehouses (with a storage height of more than 5.5 m), two initial conditions can be adopted to calculate the standard value of the dictating sprinkler flow rate:

1. With a stacking height of 5.5 m and a room height of 6.5 m.
2. With a stacking height of 12.2 m and a room height of 13.7 m.

The first reference point (minimum) is established based on the data of SP 5.131301 on the irrigation intensity and the total consumption of water AUP. For group of premises 6, the irrigation intensity is at least 0.5 l/(s m2) and the total consumption is at least 90 l/s. The consumption of a general-purpose dictating sprinkler according to the standards of SP 5.13130 ​​with such irrigation intensity is at least 6.5 l/s.

The second reference point (maximum) is established based on the data provided in the technical documentation for sprinklers [2] and ESFR [3]. With approximately equal flow rates of sprinklers -17, ESFR-17, VK503 and -25, ESFR-25, VK510 for identical warehouse characteristics, -17, ESFR-17, VK503 require higher pressure. According to [2-4], for all ESFR types (except ESFR-25), with a storage height of more than 10.7 m and a room height of more than 12.2 m, an additional level of sprinklers inside the racks is required, which requires additional consumption of fire extinguishing agent. Therefore, it is advisable to focus on the hydraulic parameters of sprinklers -25, ESFR-25, VK510.

For groups of premises 5 and 6 (according to SP 5.13130[1]) of high-rise rack warehouses, the equation for calculating the flow rate of the dictating sprinkler of water AUPs is proposed to be calculated using the formula

where

• qdict – flow rate of the dictating sprinkler depending on the stacking height and the room height, l/s;
• q5.5 – flow rate of the dictating sprinkler at a stacking height of 5.5 m and a room height of no more than 6.5 m, l/s;
• ? – coefficient of variation of the stacking height, l/(s m3);
• h – stacking height, m;
• ? – coefficient of variation of the room height, m-1;
• H – room height, m.

With a stacking height of 12.2 m and a room height of 13.7 m, the pressure at the ESFR-25 dictating sprinkler must be no less than: according to NFPA-13 [6] 0.28 MPa, according to FM 8-9 [7] and FM 2-2 [8] 0.34 MPa. Therefore, the flow rate of the dictating sprinkler for room group 6 is taken into account the pressure according to FM, i.e. 0.34 MPa:

where

• qESFR – sprinkler flow rate ESFR-25, l/s;
• КРФ – performance factor in the dimension according to GOST R 51043 [5], l/(s m of water column 0.5);
• КISO – performance factor in the dimension according to ISO 6182-7 [10], l/(min bar 0.5);
• р – sprinkler pressure, MPa.

The flow rate of the dictating sprinkler for group of rooms 5 is taken in a similar way according to formula (2) taking into account the pressure according to NFPA, i.e. 0.28 MPa — the flow rate is q10 l/s. For groups of rooms 5, the flow rate of the dictating sprinkler is q5.5 = 5.3 l/s, and for groups of rooms 6 — q5.5 = 6.5 l/s. The value of the coefficient of variation of the stacking height is given in Table 4. The value of the coefficient of variation of the room height b is given in Table 5.

The ratios of pressures given in [2, 3] with the flow rate calculated at these pressures for ESFR-25 and -25 sprinklers are presented in Table 6. The flow rate for groups 5 and 6 is calculated using formula (3). As follows from Table 7, the flow rate values ​​of the dictating sprinkler for room groups 5 and 6, calculated using formula (3), correspond quite well with the flow rate value of the ESFR-25 sprinklers, calculated using formula (2). With quite satisfactory accuracy, the difference in flow rate between room groups 6 and 5 can be taken as equal to ~ (1.1-1.2) l/s.

Thus, the initial parameters of regulatory documents for determining the total flow rate of the AUP in relation to high-rise rack warehouses in which sprinklers are placed under the cover can be:

• irrigation intensity;
• pressure at the dictating sprinkler;
• flow rate of the dictating sprinkler.

The most acceptable, in our opinion, is the flow rate of the dictating sprinkler, convenient for designers and independent of the specific type of sprinkler. It is advisable to introduce the use of the «flow rate of the dictating sprinkler» as the dominant parameter in all regulatory documents in which the irrigation intensity is used as the main hydraulic parameter.

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L. Meshman, Ph.D., Leading Researcher,
V. Bylinkin, Ph.D., Leading Researcher,
R. Gubin, Senior Researcher,
E. Romanova, Researcher